shutoff valve closure and motor operator size

[bigbirdflew]

have a question about the closure test in B16.34 and how it relates to the motor operator on a shutoff valve.

Process design conditons are (steam) approx. 20 psig and 275 degF.

valve supplier quoted a class 150# valve with a very larger motor operator; stating that to meet the closure test in B16.34 the valve operator needs to be large because B16.34 requires 110% of the 150# valve rating or approx. 110% of 285 psig. it seems to me that the operator should be sized to operate the valve against the maximum design condition, in this case 30 psig, and not the 110% requirement of closure test, which once installed the valve will never see those conditions but will have an operator sitting there just waiting for it to happen.

Are motor operators sized this way (i.e. conditions the valve will never see)? how is the closure test actually done (is the motor operator installed or does test facility somehow close the valve for the test)?

i understand what the valve supplier is saying but that seems a bit exessive for normal operating and design conditions not to mention the few extra dollars it will cost.

thanks in advance for your comments
bigbird

 

[gerhardl]

Apart from the test conditions, generally on electrical motor actuators for steam valves:

Take care for temperature limits and surrounding temperature:

1. valve to be heat isolated, actuator adapted for high temperatures, actuator sidewise eller under pipe if suitable and as needed.

2. Check longest acceptable closing and opening time, size down acctuator accordingly with mechanical gear between actuator and valve to keep size and cost down.

And the essential thing:
Actuators must be sized according to maximum expected operational torque over time. This increased torque will be depending on valvetype, design, adjustment and application, and also normally be the torque loosening valve from seat after long periodes in closed position, with or without fluid or load.

Over time this torque could easily be increased from initial required torque to considerably more, x 2 or more under unfortunate conditions and poorly managed plant.

Purely guess from my side: seems that you should discuss point 2. with the supplier, but that considerations on extra torque could be reasonable, but 110% of what? Load or what torque? And why large actuator instead of smaller plus gear? Details needed from supplier!

 

[stanier]

The problem appears to be in the Specification. The end user can define the operating conditions and specify that these supersede the requirments of the quoted standard.

A standard is not mandatory unless specified in contract or law.

If you company standards require that this standard be met then there is little you can do unless you get dispensation from those so authoirzed.

 

[bigbirdflew]

thanks

the spec did not mention B16.34 but did mention that the max diff pressure is 20 psi. so in my opinion that operator/gearing should produce enough torque to open the valve again 20 psi.

still don't know how the closure test would be performed and why anyone would want to buy a extra large operator just to pass a test at 10 times system design conditions.

 

[gerhardl]

... my point is that all real conditions should be considered, what is actually required torque to cover real normal looasening toorque over lifetime? What is actually parameters for test conditions, must valve open and close during full test pressure, yes or no? If yes, by full automatic operation by actuator and what torque to cover this, or alternative methodes?

First when this is answered your question can be answered!

Apart from this, the system (total rig) could require more than normal from the vale, but in case, this should also of course be reflected in the valve data sheet.

Conclusion: you seem to have a datasheet missing vital information, regrettably not an unusual case.

 

[bigbirdflew]

thank you for your time and pointing out the errors in the specification, however the closure test in B16.34 is still the real question.

btw;
Operating condition is approx. 15 psig
Design is 30 psig
as specified the valve would need to operate at 30 psig. so as i tried to state, providing an operator for the closure test at 314.5 psig as required in section 7.2.1 of B16.34

thanks again for your time - perhaps i am not asking my question properly

 

[reverman]

what type of valve is this? gate/globe/butterfly?

the motor should be sized for the design conditions not the one time closure test. The valve should be labeled with the design conditions it was rated for with the motor.

If we are concerned that the full closure test will damage the sized motor we will test the valve with a large gear at the normal B16.34 (api 598) pressures. Then remove the gear and mount the motor and run just a closure test at the customer design pressure to make sure the motor works properly. it's a bit of an extra step but gives everybody peace of mind that quality is good.

I can't imagine sizing every motor per the test pressure on class 1500 and 2500 valves it would be silly expensive to do that.

 

[reverman]

A possible solution to this is to tell the valve supplier you want the optional B16.34 low pressure closure test instead of the high pressure closure test. Honestly given your conditions they should be doing the low pressure closure test anyway it's much more applicable to your service.

The API 598 low pressure closure test (60-100 psi air) will be a much better simulation of your low pressure steam than a 325 psi hydro seat test.

 

[bigbirdflew]

Thanks Reverman,

i wasn't concerned about possible damage because hopefully it will be setup and tested correctly (although maybe should add a note about replacing operator with gear if needed for test) nor even cost since I’m not buying it. we need to replace an existing valve (6in to 8in)and trying to limit the modification to the existing starter (in MCC) and concerned about fitting the new valve/operator into limited space.

the valve is a globe valve. I originally posed the question because a valve supplier was stating they needed the larger operator (3 times larger than existing) because of the high pressure closure test. I didn’t realize there was an optional lower pressure test – I’ll need to do a bit more reading.

thanks again, you answered my question – didn’t see why every valve would be sized to the same pressure and like you mentioned on the high pressures it would be “silly expensive”

regards